centos7安装dnf报错ImportError: No module named _conf

在centos7系统中直接通过yum安装dnf包管理工具，使用dnf命令时报错如下：

Traceback (most recent call last):
  File "/usr/bin/dnf", line 57, in <module>
    from dnf.cli import main
  File "/usr/lib/python2.7/site-packages/dnf/__init__.py", line 30, in <module>
    import dnf.base
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 29, in <module>
    import libdnf.transaction
  File "/usr/lib64/python2.7/site-packages/libdnf/__init__.py", line 3, in <module>
    from . import conf
  File "/usr/lib64/python2.7/site-packages/libdnf/conf.py", line 17, in <module>
    _conf = swig_import_helper()
  File "/usr/lib64/python2.7/site-packages/libdnf/conf.py", line 16, in swig_import_helper
    return importlib.import_module('_conf')
  File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
ImportError: No module named _conf